Doesn't seem to just exist in improv.
An entire room full of open mikers - granted, a smaller, smarter room than is necessarily the norm - managed to riff an evening's worth of jokes on porn, after the second comic (a friend and funny, funny man) came up with a story about his wife discovering his 'real stash' of dirty goods.
Fascinating. Really fascinating. By the time I got up there (two from the end, 14th in line), the host brought me up with "I KNOW she has some material about porn."
Needless to say, I did not disappoint. You want a porn rant, you got one.
But it was neat to watch. Callback after callback, story after story, riff after riff. Regardless of preparation, pre-existing ideas. Even the baffling woman who got up and said "I'm not doing porno, sorry," and basically read the news without punchlines, she spoke of some new Paris Hilton tape.
Incidentally, a full 25% of the room were lawyers by day. Hmmm.